Gas, oil and water wells usually contain one or more well casing pipes which stretch from the surface downwards to the soil. Such pipes lie one within the other and are meant for several purposes, such as keeping the well-hole entire and governing the flow and the pressure of fluid within the well. For the purposes of this application, piping is referred to as casing if there is at least one pipe within such casing and such pipe is referred to as a pipe.
At the well-head various different kinds of well-head members are connected and sealed to the casing and the piping, and they serve several uses, among which that of supporting the casing and the piping as from the surface and that of acting as a means of linking fluid conduits to the casing as well as to the circular space created by the piping and the several casing pipes around it and that of governing the pressures of the fluid brought about in the well-head. In order to govern fluid pressures, which are often very high, seals have to be provided between the several members of the well-head and the piping and the casing. Elastomeric seals have been used for such devices which provide a seal against the piping or casing when pressure is exerted on the seal against such piping or casing. This takes place in various devices, pressure being exerted vertically on the seal, obliging it to expand internally against the piping or casing and thereby seal the latter externally. The elastomeric seal can be pushed from the inside too, by the pressure exerted upon the surface of its circumference outside. For instance, such seals have been used for many years, whereby the fluid exerts pressure in the space around the outside diameter of the elastomeric seal and thereby pushes the latter internally. The space around the seal--the annular space--is connected to the outside of the device by means of a control valve through which the fluid under pressure is introduced. In some sealing processes a liquid plastic, under pressure, is injected through the control valve to provide the seal, the plastic thereupon hardens, so that a permanent seal is provided.
Many well operators think that elastomeric seals are not to be trusted at extreme temperatures which may cause them to break down unwantedly.
The art also encompasses metallic seals as covered by U.S. Pat. No. 4353560 of Oct. 12, 1982 which refers to a metallic ring assembly to seal an annular space between the metal surfaces of concentric tubular members. The assembly consists of a central metallic sealing ring with tapering upper and lower annular flanges at both inside and outside peripheries. The sealing ring lies between adapter rings that are concentric with the sealing ring and that have bevelled annular edges that are in contact with the tapering surfaces of the sealing ring flanges, at an angle of five degrees. When pressed axially the annular flanges of the metallic sealing ring are deflected radially and their ends are bent and pushed against the surfaces of the members, thereby providing the annular space for metal to metal seals with the latter. Flanges are cut off at their loose ends which means that the initial hooking up of the adapter rings to the metallic sealing ring and the annular space around the members is by means of the annular edges at the ends of the flanges and the pressing force is concentrated at such edges. Axial loading is applied by means of screws the ends of which are worked upon by cams and there is a cam surface working upon the upper adapter ring.
In one of the aspects of this invention improvements are provided for reduction bushings for production and injection well casings.
To complete oil-producing or injectors wells on land use is made of a casing head coupled to a flanged production head, usually of the single or double completed type, upon which the Xmas tree is assembled.
The size of the upper flange of these production heads is usually 7 1/6 inch (18.2 cm) and of the lower one , 11 inches (27.94 cm) (API specification), while the inside diameter of its bottom part is 7 1/6 inches (18.2 cm), in which there are O-rings to enable sealing to take place against the top of the production casing, which is 7 inches (17.78 cm) in outside diameter, which fits into it over a distance of about 4 inches (10.16cm).
When a well is lined with 51/2 inch inside diameter pipes (13.97cm), a reduction bushing has to be employed in order to bring about the sealing between such lining and the production head. Such sealing of bushings has up to now been done by means of O-rings.